International audienceChitosan (CS) was modified by SG1-based nitroxide-mediated polymerization under heterogeneous conditions. After introduction of acrylamide and/or acrylate functions onto the CS backbone followed by intermolecular 1,2 radical addition of the BlocBuilder alkoxyamine (CS–BB), methyl methacrylate (MMA) in the presence of a small amount of acrylonitrile (AN) or sodium 4-styrenesulfonate (SS) was polymerized by nitroxide-mediated polymerization (NMP). ESR and free-solution capillary electrophoresis confirmed the synthesis of CS–BB. The successful synthesis of CS-g-P(MMA-co-AN) and CS-g-PSS grafted copolymers was proved by TGA and solid-state NMR spectroscopy with ca. 20 to 30 wt% of grafted synthetic polymer in the final product
The complexity of synthetic and natural polymers used in industrial and medical applications is expanding; thus, it becomes increasingly important to improve and develop methods for their molecular characterization. Free-solution capillary electrophoresis is a robust technique for the separation and characterization of both natural and synthetic complex charged polymers. In the case of polyelectrolytes, free-solution capillary electrophoresis is in the "critical conditions" (CE-CC): it allows their separation by factors other than molar mass for molar masses typically higher than 20000 g/mol. This method is thus complementary to size-exclusion chromatography (SEC). SEC is widely used to determine molar mass distributions and their dispersities. Utilizing CE-CC, an analogous calculation of dispersity based on the distributions of electrophoretic mobilities was derived and the heterogeneity of composition or branching in different polysaccharides or synthetic polymers was obtained in a number of experimental cases. Calculations are based on a ratio of moments and could therefore be compared to simulations of polymerization processes, in analogy to the work performed on molar mass distributions. Among four possible types of dispersity, the most precise values were obtained with the calculation analogous with the dispersity of molar mass distribution Mw/Mn. In addition, the dispersity value allows conclusions based on a single value: the closer the dispersity is to 1, the more homogeneous the polymer is in terms of composition or branching. This approach allows the analysis of dispersity of important molecular attributes of polymers other than molar mass and aims at improving the overall molecular characterization of both synthetic and natural polymers. The dispersity can also be monitored online while performing a chemical reaction within the CE instrument.
Chitosan is a biopolymer of increasing significance, as well as a renewable and sustainable material. Its main molecular characteristics are molar mass and degree of acetylation (composition). Precise average degrees of acetylation were measured by quantitative (1)H solution-state NMR spectroscopy. While number-average degrees of acetylation had already been determined by (1)H NMR spectroscopy, weight-average degrees of acetylation are also determined and may be more relevant for some properties, such as mechanical properties. We report the first separation of chitosan according to its degree of acetylation using free solution capillary electrophoresis. Capillary electrophoresis separates chitosan in the 'critical conditions': the molar mass plays little role and the separation is by the degree of acetylation. It characterises the heterogeneity of chitosan samples in terms of composition (dispersity of the distribution of degrees of acetylation). This heterogeneity (broad distribution of degrees of acetylation) cannot be neglected contrary to a common assumption found in the literature. This fast and easy separation will allow establishing a structure-property relationships.
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